Liu, “ Synchrotron-based infrared microspectroscopy under high pressure: An introduction,” Matter Radiat. Another powerful probe for investigating H–H bonds, O–H bonds, and bandgap closure metallization is infrared (IR) spectroscopy, which requires a low-emittance synchrotron IR source to enable it to be applicable to the diffraction-limited small sample sizes typical of multi-megabar studies.
report an unprecedented advance in integrating NMR with diamond anvil cell (DAC) technology that has enabled high-resolution NMR investigations of hydrogen structures and magnetism up to multi-megabar pressures, potentially leading to breakthroughs in a number of areas of high-pressure research related to hydrogen. Dubrovinsky, “ In situ high-pressure nuclear magnetic resonance crystallography in one and two dimensions,” Matter Radiat. Nuclear magnetic resonance (NMR) is one of the most sensitive techniques for probing hydrogen nuclear magnetic spins, but it has previously been impossible to use it together with high-pressure vessels. reassess the effects of a newly discovered superionic transition of hydrogen on our understanding of water storage and the water budget in the deep lower mantle.Īs hydrogen is the lightest element, with the weakest x-ray scattering cross section, experimental studies of its properties under extreme conditions pose daunting technical challenges, and this has stimulated daring attempts to obtain definitive characterizations of structures and of physical and chemical properties at high pressures. Mao, “ Role of hydrogen and proton transportation in Earth’s deep mantle,” Matter Radiat. The hydrogen chemistry controls seismic, electrical, magnetic, and mechanical properties of hydrogen-bearing rocks, and dictates water transportation and circulation in the deep interior. In the Earth’s deep interior, hydrogen in oxide minerals bonds with oxygen by OH bonding, symmetrical hydrogen bonding, and superionic bonding with increasing pressure and temperature. highlight the chemical aspects of the hydride bonding and structural motifs of LaH 10, YH 9, and CaH 6 and the effects on their pressure-induced electronic properties and superconducting mechanism above 200 K. Yang, “ Pressure-induced hydride superconductors above 200 K,” Matter Radiat. Again, reports of room-temperature superconducting hydrides are controversial owing to the difficulty of performing magnetic measurements at high pressures. Ma, “ Theory-orientated discovery of high-temperature superconductors in superhydrides stabilized under high pressure,” Matter Radiat. Although superconductivity has never been realized in pure hydrogen, various hydrogen-dominant hydrides have been predicted and observed to exhibit very high-temperature superconductivity at high pressures. Mao, “ Everything you always wanted to know about metallic hydrogen but were afraid to ask,” Matter Radiat. Metallic hydrogen has long been considered a holy grail of physics and astrophysics, but claims of hydrogen metallization under static compression are still under debate, mainly owing to the limited ability of presently available high-pressure techniques to unambiguously determine the transitions and metallization.
Hydrogen exhibits a rich physics of multiple phase transitions, including a predicted novel quantum state combining superconductivity and superfluidity upon metallization, and also provides benchmark values for testing theoretical models of quantum solids at high densities.
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